This application relates to apparatus, methods and integrated systems for detecting molecular interactions. The apparatus comprise microscale devices for moving and mixing small fluid volumes. The systems are capable of performing integrated manipulation and analysis in a variety of biological, biochemical and chemical experiments, including, e.g., DNA sequencing.
Manipulating fluidic reagents and assessing the results of reagent interactions are central to chemical and biological science. Manipulations include mixing fluidic reagents, assaying products resulting from such mixtures, and separation or purification of products or reagents and the like. Assessing the results of reagent interactions can include autoradiography, spectroscopy, microscopy, photography, mass spectrometry, nuclear magnetic resonance and many other techniques for observing and recording the results of mixing reagents. A single experiment can involve literally hundreds of fluidic manipulations, product separations, result recording processes and data compilation and integration steps. Fluidic manipulations are performed using a wide variety of laboratory equipment, including various fluid heating devices, fluidic mixing devices, centrifugation equipment, molecule purification apparatus, chromatographic machinery, gel electrophoretic equipment and the like. The effects of mixing fluidic reagents are typically assessed by additional equipment relating to detection, visualization or recording of an event to be assayed, such as spectrophotometers, autoradiographic equipment, microscopes, gel scanners, computers and the like.
Because analysis of even simple chemical, biochemical, or biological phenomena requires many different types of laboratory equipment, the modern laboratory is complex, large and expensive. In addition, because so many different types of equipment are used in even conceptually simple experiments such as DNA sequencing, it has not generally been practical to integrate different types of equipment to improve automation. The need for a laboratory worker to physically perform many aspects of laboratory science imposes sharp limits on the number of experiments which a laboratory can perform, and increases the undesirable exposure of laboratory workers to toxic or radioactive reagents. In addition, results are often analyzed manually, with the selection of subsequent experiments related to initial experiments requiring consideration by a laboratory worker, severely limiting the throughput of even repetitive experimentation.
In an attempt to increase laboratory throughput and to decrease exposure of laboratory workers to reagents, various strategies have been performed. For example, robotic introduction of fluids onto microtiter plates is commonly performed to speed mixing of reagents and to enhance experimental throughput. More recently, microscale devices for high throughput mixing and assaying of small fluid volumes have been developed. For example, U.S. Ser. No. 08/761,575 entitled xe2x80x9cHigh Throughput Screening Assay Systems in Microscale Fluidic Devicesxe2x80x9d by Parce et al. provides pioneering technology related to microscale fluidic devices, especially including electrokinetic devices. The devices are generally suitable for assays relating to the interaction of biological and chemical species, including enzymes and substrates, ligands and ligand binders, receptors and ligands, antibodies and antibody ligands, as well as many other assays. Because the devices provide the ability to mix fluidic reagents and assay mixing results in a single continuous process, and because minute amounts of reagents can be assayed, these microscale devices represent a fundamental advance for laboratory science.
In the electrokinetic microscale devices provided by Parce et al. above, an appropriate fluid is flowed into a microchannel etched in a substrate having functional groups present at the surface. The groups ionize when the surface is contacted with an aqueous solution. For example, where the surface of the channel includes hydroxyl functional groups at the surface, e.g., as in glass substrates, protons can leave the surface of the channel and enter the fluid. Under such conditions, the surface possesses a net negative charge, whereas the fluid will possess an excess of protons, or positive charge, particularly localized near the interface between the channel surface and the fluid. By applying an electric field along the length of the channel, cations will flow toward the negative electrode. Movement of the sheath of positively charged species in the fluid pulls the solvent with them.
One time consuming process is titration of biological and biochemical assay components into the dynamic range of an assay. For example, because enzyme activities vary from lot to lot, it is necessary to perform a titration of enzyme and substrate concentrations to determine optimum reaction conditions. Similarly, diagnostic assays require titration of unknown concentrations of components so that the assay can be performed using appropriate concentrations of components. Thus, even before performing a typical diagnostic assay, several normalization steps need to be performed with assay components.
Another labor intensive laboratory process is the selection of lead compounds in drug screening assays. Various approaches to screening for lead compounds are reviewed by Janda (1994) Proc. Natl. Acad. Sci. USA 91(10779-10785); Blondelle (1995) Trends Anal. Chem 14:83-91; Chen et al. (1995) Angl. Chem. Int. Engl. 34:953-960; Ecker et al. (1995) Bio/Technology 13:351-360; Gordon et al. (1994) J. Med. Chem. 37:1385-1401 and Gallop et al. (1994) J. Med. Chem. 37:1233-1251. Improvements in screening have been developed by combining one or more steps in the screening process, e.g., affinity capillary electrophoresis-mass spectrometry for combinatorial library screening (Chu et al. (1996) J. Am. Chem. Soc. 118:7827-7835). However, these high-throughput screening methods do not provide an integrated way of selecting a second assay or screen based upon the results of a first assay or screen. Thus, results from one assay are not automatically used to focus subsequent experimentation and experimental design still requires a large input of labor by the user.
Another particularly labor intensive biochemical series of laboratory fluidic manipulations is nucleic acid sequencing. Efficient DNA sequencing technology is central to the development of the biotechnology industry and basic biological research. Improvements in the efficiency and speed of DNA sequencing are needed to keep pace with the demands for DNA sequence information. The Human Genome Project, for example, has set a goal of dramatically increasing the efficiency, cost-effectiveness and throughput of DNA sequencing techniques. See, e.g., Collins, and Galas (1993) Science 262:43-46.
Most DNA sequencing today is carried out by chain termination methods of DNA sequencing. The most popular chain termination methods of DNA sequencing are variants of the dideoxynucleotide mediated chain termination method of Sanger. See, Sanger et al. (1977) Proc. Nat. Acad. Sci., USA 74:5463-5467. For a simple introduction to dideoxy sequencing, see, Current Protocols in Molecular Biology, F. M. Ausubel et al., eds., Current Protocols, a joint venture between Greene Publishing Associates, Inc. and John Wiley and Sons, Inc., (Supplement 37, current through 1997) (Ausubel), Chapter 7. Four color sequencing is described in U.S. Pat. No. 5,171,534. Thousands of laboratories employ dideoxynucleotide chain termination techniques. Commercial kits containing the reagents most typically used for these methods of DNA sequencing are available and widely used.
In addition to the Sanger methods of chain termination, new PCR exonuclease digestion methods have also been proposed for DNA sequencing. Direct sequencing of PCR generated amplicons by selectively incorporating boronated nuclease resistant nucleotides into the amplicons during PCR and digestion of the amplicons with a nuclease to produce sized template fragments has been proposed (Porter et al. (1997) Nucleic Acids Research 25(8): 1611-1617). In the methods, 4 PCR reactions on a template are performed, in each of which one of the nucleotide triphosphates in the PCR reaction mixture is partially substituted with a 2xe2x80x2deoxynucleoside 5xe2x80x2-xcex1[P-borano]triphosphate. The boronated nucleotide is stocastically incorporated into PCR products at varying positions along the PCR amplicon in a nested set of PCR fragments of the template. An exonuclease which is blocked by incorporated boronated nucleotides is used to cleave the PCR amplicons. The cleaved amplicons are then separated by size using polyacrylamide gel electrophoresis, providing the sequence of the amplicon. An advantage of this method is that it requires fewer biochemical manipulations than performing standard Sanger-style sequencing of PCR amplicons.
Other sequencing methods which reduce the number of steps necessary for template preparation and primer selection have been developed. One proposed variation on sequencing technology involves the use of modular primers for use in PCR and DNA sequencing. For example, Ulanovsky and co-workers have described the mechanism of the modular primer effect (Beskin et al. (1995) Nucleic Acids Research 23(15):2881-2885) in which short primers of 5-6 nucleotides can specifically prime a template-dependent polymerase enzyme for template dependent nucleic acid synthesis. A modified version of the use of the modular primer strategy, in which small nucleotide primers are specifically elongated for use in PCR to amplify and sequence template nucleic acids has also been described. The procedure is referred to as DNA sequencing using differential extension with nucleotide subsets (DENS). See, Raja et al. (1997) Nucleic Acids Research 25(4):800-805.
In addition to enzymatic and other chain termination sequencing methods, sequencing by hybridization to complementary oligonucleotides has been proposed, e.g., in U.S. Pat. No. 5,202,231, to Drmanac et al. and, e.g., in Drmanac et al. (1989) Genomics 4:114-128. Chemical degradation sequencing methods are also well known and still in use; see, Maxam and Gilbert (1980) in Grossman and Moldave (eds.) Academic Press, New York, Methods in Enzymology 65:499-560.
Improvements in methods for generating sequencing templates have also been developed. DNA sequencing typically involves three steps: i) making suitable templates for the regions to be sequenced; ii) running sequencing reactions for electrophoresis and iii) assessing the results of the reaction. The latter steps are sometimes automated by use of large and very expensive workstations and autosequencers. The first step often requires careful experimental design and laborious DNA manipulation such as the construction of nested deletion mutants. See, Griffin, H. G. and Griffin, A. M. (1993) DNA sequencing protocols, Humana Press, New Jersey. Alternatively, random xe2x80x9cshot-gunxe2x80x9d sequencing methods, are sometimes used to make templates, in which randomly selected sub clones, which may or may not have overlapping sequence information, are randomly sequenced. The sequences of the sub clones are compiled to produce an ordered sequence. This procedures eliminates complicated DNA manipulations; however, the method is inherently inefficient because many recombinant clones must be sequenced due to the random nature of the procedure. Because of the labor intensive nature of sequencing, the repetitive sequencing of many individual clones dramatically reduces the throughput of these sequencing systems.
Recently, Hagiwara and Curtis (1996) Nucleic Acids Research 24(12):2460-2461 developed a xe2x80x9clong distance sequencerxe2x80x9d PCR protocol for generating overlapping nucleic acids from very large clones to facilitate sequencing, and methods of amplifying and tagging the overlapping nucleic acids into suitable sequencing templates. The methods can be used in conjunction with shotgun sequencing techniques to improve the efficiency of shotgun methods.
Although improvements in robotic manipulation of fluidic reagents and miniaturization of laboratory equipment have been made, and although particular biochemical processes such as DNA sequencing and drug screening are very well developed, there still exists a need for additional techniques and apparatus for mixing and assaying fluidic reagents, for integration of such systems and for reduction of the number of manipulations required to perform biochemical manipulations such as drug screening and DNA sequencing. Ideally, these new apparatus would be useful with, and compatible to, established biochemical protocols. This invention provides these and many other features.
This invention provides apparatus, systems and methods for integrated manipulation and analysis of fluidic reagents. The integrated features provide very high throughput methods of assessing biochemical components and performing biochemical manipulations. A wide variety of reagents and products are suitably assessed, including libraries of chemical or biological compounds or components, nucleic acid templates, PCR reaction products, and the like. In the integrated systems it is possible to use the results of a first reaction or set of reactions to select appropriate reagents, reactants, products, or the like, for additional analysis. For example, the results of a first sequencing reaction can be used to select primers, templates or the like for additional sequencing, or to select related families of compounds for screening in high-throughput assay methods. These primers or templates are then accessed by the system and the process continues.
In one aspect, the invention provides integrated methods of analyzing and manipulating sample materials for fluidic analysis. In the methods, an integrated microfluidic system including a microfluidic device is provided. The device has at least a first reaction channel and at least a first reagent introduction channel, typically etched, machined, printed, or otherwise manufactured in or on a substrate. Optionally, the device can have a second reaction channel and/or reagent introduction channel, a third reaction channel and/or reagent introduction channel or the like, up to and including hundreds or even thousands of reaction and/or reagent introduction channels. The reaction channel and reagent introduction channels are in fluid communication, i.e., fluid can flow between the channels under selected conditions. The device has a material transport system for controllably transporting a material through and among the reagent introduction channel and reaction channel. For example, the material transport system can include electrokinetic, electroosmotic, electrophoretic or other fluid manipulation aspects (micro-pumps and microvalves, fluid switches, fluid gates, etc.) which permit controlled movement and mixing of fluids. The device also has a fluidic interface in fluid communication with the reagent introduction channel. Such fluidic interfaces optionally include capillaries, channels, pins, pipettors, electropipettors, or the like, for moving fluids, and optionally further include microscopic, spectroscopic, fluid separatory or other aspects. The fluidic interface samples a plurality of reagents or mixtures of reagents from a plurality of sources of reagents or mixtures of reagents and introduces the reagents or mixtures of reagents into the reagent introduction channel. Essentially any number of reagents or reagent mixtures can be introduced by the fluidic interface, depending on the desired application. Because microfluidic manipulations are performed in a partially or fully sealed environment, contamination and fluidic evaporation in the systems are minimized.
In the methods, a first reagent from the plurality of sources of reagent or mixtures of reagents is selected. A first sample material and the first reagent or mixture of reagents is introduced into the first reaction channel, whereupon the first sample material and the first reagent or mixture of reagents react. This reaction can take a variety of different forms depending on the nature of the reagents. For example, where the reagents bind to one another, such as where the reagents are an antibody or cell receptor and a ligand, or an amino acid and a binding ligand, the reaction results in a bound component such as a bound ligand. Where the reagents are sequencing reagents, a primer extension product results from the reaction. Where the reagents include enzymes and enzyme substrates, a modified form of the substrate typically results. Where two reacting chemical reagents are mixed, a third product chemical typically results.
In the methods, a reaction product of the first sample material and the first reagent or mixture of reagents is analyzed. This analysis can take any of a variety of forms, depending on the application. For example, where the product is a primer extension product, the analysis can take the form of separating reactants by size, detecting the sized reactants and translating the resulting information to give the sequence of a template nucleic acid. Similarly, because microscale fluidic devices of the invention are optionally suitable for heating and cooling a reaction, a PCR reaction utilizing PCR reagents (thermostable polymerase, nucleotides, templates, primers, buffers and the like) can be performed and the PCR reagents detected. Where the reaction results in the formation of a new product, such as an enzyme-substrate product, a chemical species, or an immunological component such as a bound ligand, the product is typically detected by any of a variety of detection techniques, including autoradiography, microscopy, spectroscopy, or the like.
Based upon the reaction product, a second reagent or mixture of reagents is selected and a second sample material is assessed. For example, where the product is a DNA sequence, a sequencing primer and/or template for extension of available sequence information is selected. Where the product is a new product such as those above, an appropriate second component such as an enzyme, ligand, antibody, receptor molecule, chemical, or the like, is selected to further test the binding or reactive characteristics of an analyzed material. The second reagent or mixture of reagents is introduced into the first reaction channel, or optionally into a second (or third or fourth . . . or nth) reaction channel in the microfluidic device. The second sample material and the second reagent or mixture of reagents react, forming a new product, which is analyzed as above. The results of the analysis can serve as the basis for the selection and analysis of additional reactants for similar subsequent analysis. The second sample material, reagents, or mixtures of reagents can comprise the same or different materials. For example, a single type of DNA template is optionally sequenced in several serial reactions. Alternatively, completing a first sequencing reaction, as outlined above, serves as the basis for selecting additional templates (e.g., overlapping clones, PCR amplicons, or the like).
Accordingly, in a preferred aspect, the invention provides methods of sequencing a nucleic acid. In the methods, the biochemical components of a sequencing reaction (e.g., a target nucleic acid, a first and optionally, second sequencing primer, a polymerase (optionally including thermostable polymerases for use in PCR), dNTPs, and ddNTPs) are mixed in a microfluidic device under conditions permitting target dependent polymerization of the dNTPs. Polymerization products are separated in the microfluidic device to provide a sequence of the target nucleic acid. Typically, sequencing information acquired by this method is used to select additional sequencing primers and/or templates, and the process is reiterated. Generally, a second sequencing primer is selected based upon the sequence of the target nucleic acid and the second sequencing primer is mixed with the target nucleic acid in a microfluidic device under conditions permitting target dependent elongation of the selected second sequencing primer, thereby providing polymerization products which are separated by size in the microfluidic device to provide further sequence of the target nucleic acid. As discussed above, the systems for mixing the biochemical sequencing components, separating the reaction products, and assessing the results of the sequencing reaction are integrated into a single system.
In one integrated sequencing system, methods of sequencing a target nucleic acid are provided in which an integrated microfluidic system comprising a microfluidic device is utilized in the sequencing method. The integrated microfluidic device has at least a first sequencing reaction channel and at least a first sequencing reagent introduction channel, the sequencing reaction channel and sequencing reagent introduction channel being in fluid communication. The integrated microfluidic system also has a material transport system for controllably transporting sequencing reagents through the sequencing reagent introduction channel and sequencing reaction channel and a fluidic interface in fluid communication with the sequencing reagent introduction channel for sampling a plurality of sequencing reagents, or mixtures of sequencing reagents, from a plurality of sources of sequencing reagents or mixtures of sequencing reagents and introducing the sequencing reagents or mixtures of sequencing reagents into the sequence reagent introduction channel. As discussed above, the interface optionally includes capillaries, pins, pipettors and the like. In the method, a first sequencing primer sequence complementary to a first subsequence of a first target nucleic acid sequence is introduced into the sequence reagent introduction channel. The first primer is hybridized to the first subsequence and the first primer is extended with a polymerase enzyme along the length of the target nucleic acid sequence to form a first extension product that is complementary to the first subsequence and a second subsequence of the target nucleic acid. The sequence of the first extension product is determined and, based upon the sequence of the first extension product, a second primer sequence complementary to a second subsequence of the target nucleic acid sequence is selected, hybridized and extended as above.
In the sequence methods herein, it is sometimes advantageous to have select sequencing primers from a large set of sequencing primers, rather than synthesizing primers to match a particular target nucleic acid. For example, 5 or 6-mer primers can be made to hybridize specifically to a target, e.g., where the primers are modular and hybridize to a single region of a nucleic acid. All possible 5 or 6 mers can be synthesized for selection in the methods herein, or any subset of 5 or 6 mers can also be selected. In some embodiments, the primers are transferred to the microfluidic apparatus, e.g., by a capillary, an electropipettor, or using sipping technology, from a microtiter plate or from and array of oligos. In other embodiments, the primers are located on a region of a microfluidic device, chip or other substrate.
An advantage of these sequencing methods is that they dramatically increase the speed with which sequencing reactions can be performed. An entire sequencing reaction, separation of sequencing products and sequence generation can be performed in less than an hour, often less than 30 minutes, generally less than 15 minutes, sometimes less than 10 minutes and occasionally less than 5 minutes.
The present invention provides integrated systems and apparatus for performing the sequencing methods herein. In one embodiment, the invention provides a sequencing apparatus. The apparatus has a top portion, a bottom portion and an interior portion. The interior portion has at least two intersecting channels (and often tens, hundreds, or thousands of intersecting channels), wherein at least one of the two intersecting channels has at least one cross sectional dimension between about 0.1 xcexcm and 500 xcexcm. A preferred embodiment of the invention includes an electrokinetic fluid direction system for moving a sequencing reagent through at least one of the two intersecting channels. The apparatus further includes a mixing zone fluidly connected to the at least two intersecting channels for mixing the sequencing reagents, and a size separation zone fluidly connected to the mixing zone for separating sequencing products by size, thereby providing the sequence of a target nucleic acid. Optionally, the apparatus has a sequence detector for reading the sequence of the target nucleic acid. In one preferred embodiment, the apparatus has a set of wells for receiving reagents such as primer sets for use in the apparatus. In one embodiment, the apparatus has at least 4,096 wells fluidly connected to the at least two intersecting channels. Alternatively, the apparatus can include a substrate (matrix, or membrane) with primers located on the substrate. Often, the primers will be dried in spots on the substrate. In this embodiment, the apparatus will typically include an electropipettor which has a tip designed to re-hydrate a selected spot corresponding to a dried primer, and for electrophoretic transport of the rehydrated primer to an analysis region in the microfluidic device (i.e., a component of the microfluidic device which includes a reaction channel). Thus, in a preferred embodiment, the device will include a substrate such as a membrane having, e.g., 4,096 spots (i.e., all possible 6-mer primers). Similarly, components in diagnostic or drug screening assays can be stored in the well or membrane format for introduction into the analysis region of the device. Arrays of nucleic acids, proteins and other compounds are also used in a similar manner.
In another embodiment, the invention provides systems for determining a sequence of nucleotides in a target nucleic acid sequence. The system includes a microfluidic device having a body structure with at least a first mixing or analysis channel, and at least a first probe introduction channel disposed therein, the analysis channel intersecting and being in fluid communication with the probe introduction channel. The system includes a source of the target nucleic acid sequence in fluid communication with the analysis channel and a plurality of separate sources of oligonucleotide probes in fluid communication with the probe introduction channel, each of the plurality of separate sources containing an oligonucleotide probe having a different nucleotide sequence of length n. Typically, all or essentially all (i.e., most, i.e., at least about 70%, typically 90% or more) of the possible oligonucleotides of a given length are included, although a subset of all possible oligonucleotides can also be used. The system also includes a sampling system for separately transporting a volume of each of the oligonucleotide probes from the sources of oligonucleotide probes to the probe introduction channel and injecting each of the oligonucleotide probes into the analysis channel to contact the target nucleic acid sequence and a detection system for identifying whether each oligonucleotide probe hybridizes with the target nucleic acid sequence.
Methods of using the system for sequencing by hybridization to perfectly matched probes are also provided. In these methods, a target nucleic acid is flowed into the analysis channel and a plurality of extension probes are separately injected into the analysis channel, whereupon the extension probes contact the target nucleic acid sequence. In the method, a first subsequence of nucleotides in the target nucleic acid is typically known, and each of the plurality of extension probes has a first sequence portion that is perfectly complementary to at least a portion of the first subsequence, and an extension portion that corresponds to a portion of the target nucleic acid sequence adjacent to the target subsequence, the extension portion having a length n, and comprising all possible nucleotide sequences of length n, wherein n is between 1 and 4 inclusive. A sequence of nucleotides is identified adjacent the target subsequence, based upon which of the plurality of extension probes perfectly hybridizes with the target nucleic acid sequence.